it was --------that she could notfinish it by herselfa,so difficult a work b,such a difficult workc,so difficult workd,such diffficult work加解析 work是可数名词吗？怎样判断

b
从后半句可以看得出，it指代前面提到过的work,而work是可数名词，就得用such a修饰。

B
1)such＋a(an)＋adj.＋单数可数名词＋that…clause
He is such a clever boy that everybody likes him.
他非常聪明，大家都非常喜欢他。
He was such an honest man that he was praised by the teacher.
他非常诚实，因而受到了老师的表扬。
2)such＋adj.＋复数可数名词＋that…clause
They are such interesting novels that I want to read them once again.
这些小说非常有趣，我想再读一遍。
3)such＋adj.＋不可数名词＋that…clause
He has made such great progress that the teachers are pleased with him.
他进步得很快，老师们对他感到很满意。
注意：如果such后边的名词前由many、much、few、little等词所修饰的话，则不用
such而用so。例如：
He had so many falls that he was black and blue all over.
他摔了很多跤，以致于全身上下青一块，紫一块的。
He had so little education that he was unfit for this job.
他所受教育很少，不适合做这个工作。
There were so many people in the street watching the fire that firefighters could not get close to
the building.
街上有那么多人观看大火，以致于消防队员无法接近大楼。
6.In fact, his English is one of these articles was so good that Engels wrote him a letter and
praised him for it.
事实上，在那些文章中有一篇他的英文写得很好，恩格斯曾写信赞扬他。
so…that也作“如此…以致”解，连接一个表示结果的状语从句。so…that与such…
that意思相同，但用法不同。现将so…that用法总结如下：
so＋adj.／adv.＋that…clause（so的后面跟形容词或副词）
He runs so fast that nobody can catch up with him.
他跑得非常快，没人能追上他。
Dr. Wang is so good that everybody loves and respects him. (=He is so good a doctor that
everybody loves and respects him. =He is such a good doctor that everybody loves and respects him.)
他是一位好医生，大家都尊敬并爱戴他。

d
work做工作时是不可数名词,因此所修饰前面不能加不定冠词a,
这样首先将a,b选项排除
剩下c,d
很容易选择d
such＋adj.＋不可数名词＋that…clause
注意：如果such后边的名词前由many、much、few、little等词所修饰的话,则不用
such而用so.

B
such a 是词组，固定的